text: Kapustinskii originally proposed the following simpler form, which he faulted as "associated with antiquated concepts of the character of repulsion forces". 
  Here, K. This form of the Kapustinskii equation may be derived as an approximation of the Born–Landé equation, below. 
  Kapustinskii replaced r, the measured distance between ions, with the sum of the corresponding ionic radii. In addition, the Born exponent, n, was assumed to have a mean value of 9. Finally, Kapustinskii noted that the Madelung constant, M, was approximately 0.88 times the number of ions in the empirical formula. The derivation of the later form of the Kapustinskii equation followed similar logic, starting from the quantum chemical treatment in which the final term is  where d is as defined above. Replacing r as before yields the full Kapustinskii equation.